Liquid inker for electrographic image development employing the suction of an air pump for applying the ink



' July 16, 1968 w. A. LLOYD I 3,392,706

LIQUID INKER FOR ELECTROGRAPHIC IMAGE DEVELOPMENT EMPLOYING THE SUCTION OF AN AIR PUMP FOR APPLYING THE INK Filed Sept. 1966 2 Sheets-Sheet 1 INVENTOR.

WILL A. LLOYD l Md ATTORNF Y July 16, 1968 w. A. LLOYD 3,392,706

LIQUID INKER FOR ELECTROGRAPHIC IMAGE DEVELOPMENT EMPLOYING THE SUCTION OF AN AIR PUMP FOR APPLYING THE INK Filed Sept. 6, 1966 2 Sheets-Sheet 2 I'll/I III RNEY

WILLI A.LLOYD I BY L3 wk T0 United States Patent LIQUID lNKER FOR ELECTROGRAPHIC IMAGE DEVELOPMENT EMPLOYING THE SUCTION OF AN AIR PUMP FOR APPLYING THE INK William A. Lloyd, San Jose, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Sept. 6, 1966, Ser. No. 577,443 Claims. (Cl. 118-637) ABSTRACT OF THE DISCLOSURE A liquid inker for developing electrographic charge images on a recording web is disclosed. The liquid inker includes a liquid inking channel having an inking slot in one side wall thereof for inking electrostatic images on an electrographic recording web to be developed. The inking channel is in liquid communication with a reservoir containing a supply of liquid ink. The suction intake of an air pump is connected into the inking channel for establishing a subatmospheric pressure head on the inking channel relative to the pressure head on the ink reservoir for drawing liquid ink from the reservoir into the inking channel. The subatmospheric pressure head generated on the inking channel causes the image bearing web to form a fluid tight seal around the marginal edges of the inking slot, thereby preventing escape of the ink and permitting the ink to be liberally applied to the charge image passing the slot for developing same. Provisions are made in the inking system for limiting the suction pressure at the intake of the air pump relative to the pressure on the reservoir such that the suction is insuflicient to cause liquid ink to be drawn from the reservoir into the intake of the air pump.

Heretofore, liquid inkers for electrographic printing have been developed wherein the suction of a liquid pump, which pumped the ink slurry, served to draw the ink into contact with a moving web bearing the electrostatic images to be inked (developed). In this prior inker an elongated hollow channel member having a slot opening along one side had an input port at one end of the channel and an output port at the other end. A moving web, bearing the electrostatic images to be developed, was passed transversely of the slot with the electrostatic images facing the open slot. A liquid pump was connected with its suction side to the output port of the channel to draw liquid ink from a reservoir through the channel and to return the ink to the reservoir. The suction applied to the channel caused the image bearing web to be drawn against the slot and thus to seal the marginal edges of the slot in the channel to prevent unwanted leakage of the ink. The exit edge of the slot provided a squeegee action to remove excess ink from the web as it passed across the inking slot.

In the inking process, minute particles of pigment, which are suspended in a quick drying dielectric liquid vehicle of the ink, are passed adjacent the electrostatic images on the web. The pigment particles, such as carbon, are pulled out of suspension and held substantially only to the charge image portions of the web. The squeegee action of the inking slot does not smear or remove the deposited pigment. The web is then dried and the pigment particles remain afiixed only to the image areas of the web, thereby inking or developing same.

In such a prior art system the suction on the web varies greatly in an erratic fashion due to air bubbles drawn into the intake of the pump through the slot in the inking channel before an adequate seal can be achieved between the web and the marginal edges of the inking slot. In addition, the life of the pump and, thus, the reliability of the 3,392,706 Patented July 16, 1968 ICC inking slot and the image bearing web, whereby the pumpdoes not have to directly pump the ink slurry, thereby increasing the operating life and reliability of the inker. In a preferred embodiment of the present invention, air bubles are introduced into a liquid passageway of the inking system and serve to produce circulation and agitation of the ink to renew the supply of pigment particles to the inking slot.

The principal object of the present invention is the provision of an improved liquid inker for electrographic devices.

One feature of the present invention is the pro-vision of an air pump for reducing the air pressure on the liquid ink supply within the inking channel, whereby the image bearing web is pushed in against the inking slot by the atmosphere without the pump having to directly pump the ink slurry thereby extending the operating life and improving the reliability of the electrographic inker.

Another feature of the present invention is the same as the preceding feature including the provision of means for bleeding air bubbles into one of the ink supply passageways between the ink reservoir and the inking slot, whereby the bubbles produce a circulation of ink between the reservoir and the inking slot to renew the supply of inking particles to the inking slot.

Another feature of the present invention is the same as any one or more of the preceding features wherein the liquid inker includes an inking slot chamber portion interconnected by a liquid passageway to a lower reservoir chamber portion with the air pump connected to reduce the air pressure in the inking slot chamber relative to the air pressure in the reservoir to draw a portion of the liquid ink from the reservoir up into the inking slot chamber, and wherein a float controlled air by-pass valve is provided for regulating the air pressure differential between the air pressure in the reservoir chamber and the air pressure in the inking slot chamber to regulate the height of the ink column in the inking chamber.

Another feature of the present invention is the same as any one or more of the preceding including the provision of an air pressure control valve for regulating the reduced air pressure in the inker, whereby the suction on the web in the inking chamber is regulated.

Another feature of the present invention is the same as any one or more of the preceding features wherein the air pump is an air blower with the output of the air blower being directed on the inked web to accelerate drying thereof.

Other features and advantages of the present invention will become apparent upon a perusal 'of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic perspective view, partially broken away, of an electrographic recorder apparatus employing features of the present invention,

FIG. 2 is an enlarged sectional view of the recorder of FIG. 1 taken along line 22 in the direction of the arrows,

FIG. 3 is a sectional view of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows,

FIG. 4 is a sectional view of the structure of FIG. 3 taken along line 4-4 in the direction of the arrows,

FIG. 5 is a sectional view similar to that of FIG. 2 depicting an alternative embodiment of the present invention, and

FIG. 6 is a sectional view of the structure of FIG. taken along line 6-6 in the direction of the arrows.

Referring now to FIG. 1 there is shown an electrographic recorder 1 employing the inker of the present invention. The recorder 1 is of a conventional self-balancing potentiometer type modified by replacing the conventional inking pen with an electrostatic writing stylus 2 having a potential of -400 v. to l000 v. applied thereto relative to a conductive base plate member 3. Electrographic paper 4 with its dielectric surface adjacent the stylus 2 is passed between the stylus 2 and the base plate 3. The lateral position of the stylus 2 on the paper 4 is determined by balance of the potentiometer circuit of the recorder 1 in response to the input signal to be recorded which is applied to the input terminals 5 of the recorder 1.

The electrographic paper 4 or web is preferably of the type formed by a conductive paper backing coated on the writing surface with a dielectric film. Such a paper is commercially available from Crown Zellerbach. The paper 4 is continuously supplied to the writing stylus 2 from a roll 6 and drawn from the roll via a pair of motor driven sprockets 7 which engage rows of perforations in the side margins of the paper 4. Alternatively, the paper could be pulled by a pair of motor driven friction wheels, not shown.

The stylus 2 lays down on the paper 4 an electrostatic charge image 8 which represents a graphic display of the signal being recorded. A liquid inking channel 9, more fully described below, in fluid communication with an ink reservoir 11 applies a fast drying electrographic ink to the charge image pattern 8 for inking (developing) same, as shown by 8. An air pump 12 with its suction connected to the channel 9 reduces the air pressure in the channel relative to the air pressure on the liquid in the reservoir thereby causing the liquid to be pushed up into the channel 9.

A suitable electrographic ink comprises a 2% to 4% solution by volume of an office copy toner concentrate, such as that marketed by Philip A. Hunt Chemical Co. or Plastic Coating Corp., in an odorless paint thinner, such as Shell Solvent #72 available from Shell Chemical Corp.

Referring now to FIGS. 2-4 the inker of the present invention is described in greater detail. The inking channel 9 comprises a hollow rectangular block 13 as of Lucite 7.75 long by 1.5" high by 0.750 wide. The block 13 is hollowed out to provide a rectangular inking chamber 17 as of 5.5" in length by 1.25" in height by 0.375" in width. The lower side of the inking chamber is open to the outside of the block 13 to define an inking slot 15 as of 0.375 wide and 5.5" long.

The ink reservoir 11 as of 1.0" in height by 9.5" in length and 3.0" in width is disposed beneath the inking channel 9 and in liquid communication with the inking chamber 14 via a pair of liquid passageways 16 each including tubular portions 17 as of 7 ID. extending down into the reservoir 11. The web 4 to be inked as of 6" in width is passed across the slot 15 with the electrostatic image 8 adjacent the slot 15.

The suction side of the air pump 12 is connected by tubulation 20, as of 7 diameter, into the top portion of inking chamber 14. The air pump 12, in this embodiment, preferably draws a suction of between and inches of water. With the web 4 in place across the inking slot 15, the suction of the air pump 12 reduces the air pressure in the inking chamber 14 causing ink in the reservoir 11 to be drawn up into the inking chamber 14 through passageways 16. When the liquid level in the inking chamber 14 has reached a suitable predetermined level 21 such as 0.75" above the level of the slot 15, a float controlled air by-pass valve 18 is opened permitting the suction of the pump 12 to be applied to the air space in the reservoir chamber 11 via an interconnecting gas passageway 19 as of 0.125" diameter and 3.0" in length.

When the by-pass valve 18 is opened the liquid level in the inking chamber 14 will not rise as the air pressure is reduced on the liquid in the reservoir 11 to a valve just suflicient to support the predetermined float controlled liquid level 21 in the inking chamber 14.

The float controlled by-pass valve assembly includes a rod shaped float 22 as of 0.350" diameter Lucite rod 3" in length. The lower end of the rod 22 is hollow to contain a closed air chamber 23. The rod 22 is freely pivoted about a pin 24 which passes transversely of the inking chamber 14 above the liquid level 21. The upper end of the float rod 22 at 25 is provided with a flat surface which mates with the by-pass valve 18 to close off the valve 18 when the float rod 22 is below the predetermined liquid level 21.

A pressure regulator valve 26, such as provided by a variable air leak or air bleeder is connected into the air chamber of the reservoir 11 for controlling the total suction pressure on the inking system. The pressure regulator valve 26 could equally well have been placed in direct gas communication with the air chamber in the inking chamber 14, as indicated by phantom lines 26'. The suction pressure on the slot 15 in the inking chamber 14 is approximately the pressure on the liquid in the reservoir 11. The pressure regulator is adjusted for the speed of the air pump 12 to produce the desired suction on the inking slot 15. For the typical inking application of a continuously moving web 4, this suction falls within the range of minus 1 to minus 15 inches of water. The faster the speed of the web 4 across the slot 15 the greater should be the suction to obtain increased squeegee action for wiping the web 4 dry.

A second air passageway 27 is connected through the wall of the reservoir 11 to bleed outside air into the base of one of the tubular fluid passageways 17 between the reservoir 11 and the inking chamber 14. An adjustable valve 28 controls the air flow into the passageway 17. The air bubbles which rise through the passageway 17 and into the inking chamber 14 produce an upward flow of ink on one side of the reservoir 11 and inking chamber 14. The result is a fluid circulation from the reservoir 11 through the inking chamber 14 and back to the reservoir 11 as indicated by the arrows 29. This circulation of ink serves to renew the supply of ink pigment from the reservoir 11 to the inking slot 15. In addition, the bubbles and fluid circulation serve to agitate the ink to retain the ink pigment in suspension.

Referring now to FIGS. 5 and 6 there is shown an alternative embodiment of the present invention which is similar to the embodiment of FIGS. l-4 except that the air pump 12 is replaced by an air blower 31 type of air pump, the reservoir 11 is open to atmospheric pressure, and the output air flow from the blower 31 is applied to the web 4 to enhance drying of the web 4.

In this embodiment the air blower 31 is driven by an electrical motor 32. The suction of the blower 31 is connected into the air chamber portion of the inking channel 13 via air passageway 33. Typical air blowers 31 which are suitable for this use produce a suction pressure of from minus 3 to minus 10 inches of water. The reservoir 11 is open on its top 34 to the atmosphere. The tubular portions 17 of the liquid passageways 16 between the inking chamber 13 and reservoir 11 are longer than those of the previous embodiment of FIGS. 1-4 because the suction pressure on the web 4 at the inking slot 15 is equal to the height of the liquid column between the liquid level in the reservoir and the height of the inking slot 15. Thus, if it were desired to have minus 7 inches of suction pressure on the web 4 the liquid level in the reservoir would have to be 7 inches below the level of the inking slot 15. Such a height is suitable for many applications. However, for low profile portable electrographic recorders it is preferred to use a closed reservoir 11 as described with regard to FIGS. 1-4. The ink is circulated and agitated by the air bubbles which are introduced into the tubular fluid passageway portions 17 via air leak 27 and valve 28 as previously described.

The air blower 31 has a second main input duct 35, co axial with the suction duct 33, which provides the major portion of the input air flow to the blower 31. The output air flow of the blower 31 is directed via an output duct 37 onto the inked web 4 as it passes beyond the inker 9. This additional air flow over the moist web 4 serves to accelerate drying of the web 4. The air blower 31 has advantages of simplicity as compared to the alternative embodiment of FIGS. 14 in that the air blower type of air pump is self regulating as to its suction pressure to provide a nearly constant and predetermined suction pressure. As a result the float valve control of an air by-pass is not required for controlling the liquid level in the inking chamber 14.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an electrographic inking apparatus, means forming a reservoir for containing an electrographic ink slurry, means forming an inking channel in liquid communication with said reservoir, said inking channel having a slot along one side thereof for applying electrographic ink to a web traversing said slot and which web contains latent electrostatic images to be developed, the improvement comprising, means forming an air pump having an air suction intake, means forming a fluid conduit interconnecting said suction intake of said air pump and said inking channel for producing a subatmospheric pressure head on said inking channel relative to the pressure head on said reservoir to draw liquid ink from said reservoir means into said inking channel and for drawing the web into contact with the liquid ink in the slot of said inking channel, means establishing the relative subatmospheric pressure head developed between said suction intake of said air pump and said reservoir to an amount sufficiently great to cause the liquid ink to be drawn from said reservoir into said inking channel but insufficient to draw liquid ink from said reservoir and inking channel into said suction intake of said air pump, whereby electrographic ink is applied to the web for developing latent electrostatic charge images on the web without said air pump having to directly pump the ink slurry.

2. The apparatus of claim 1 wherein the inking slot of said inking channel is disposed above the level of the ink in said reservoir, and said air pump serves to reduce the air pressure on the liquid in said inking channel, relative to the air pressure on the ink in said reservoir to draw the ink up into said inking channel from said reservoir.

3. The apparatus of claim 2 including means forming a pair of liquid passageways providing the liquid communication between said inking channel and said reservoir, and means for introducing air into one of said liquid passageways to produce a rising stream of bubbles in said one passageway and thus to produce a circulation of liquid ink between said reservoir and said inking channel for renewing the supply of ink to said inking channel.

4. The apparatus of claim 2 wherein said air pump is an air blower, and means for directing the output air flow of said air blower against the inked web for drying the web.

5. The apparatus of claim 2 wherein said reservoir comprises a substantially closed chamber which operates with less than 1 atmosphere of air pressure on the liquid ink in said reservoir with the suction of said air pump applied to said inking channel, whereby the height of the operating liquid ink column as drawn into said inking channel in use can be substantially reduced as compared to the height of the ink column required for a given suction on the inking channel of said reservoir operated at 1 atmosphere of pressure on the liquid ink therein.

6. The apparatus of claim 5 including means forming a by-pass air passageway communicating between the suction air pressure regions of said reservoir and said inking channel, and means forming an air valve in said by-pass air passageway and actuated by the liquid ink level in said inking channel for controlling the air flow through said by-p'ass air passageway to maintain a predetermined liquid level in said inking channel.

7. The apparatus of claim 5 including means forming an outside air passageway between the outside air and the suction air pressure region within the system comprised of said interconnected inkingchannel and reservoir, and means in said outside air passageway for throttling the flow of air from the outside through said outside air passageway to a predetermined flow rate to maintain a predetermined suction on said inking channel and the web to be inked.

8. The apparatus of claim 6 including a float for floating on the liquid in said inking channel to actuate said by-pass control valve.

9. The apparatus of claim 2 including means for applying electrostatic charge images to the web, and means for producing relative movement between the web and said inking channel for developing image patterns substantially larger than the dimensions of the inking slot.

10. The apparatus of claim 7 wherein said throttling means is adjustable for variably adjusting the suction on said web in said inking channel.

References Cited UNITED STATES PATENTS 2,856,848 10/1958 Pritchard.

2,956,494 10/1960 Tyler et al. --89 XR 2,998,802 9/1961 Harris et al. 118-637 3,005,726 10/1961 Olson 118-637 XR 3,063,868 11/1962 Brandsma et al. 11863 XR 3,081,687 3/1963 Takats 95-89 3,277,493 10/1966 Fyler 118410 XR CHARLES A. WILLMUTH, Primary Examiner.

PETER FELDMAN, Examiner. 

